first of all thank you all for comments and help.
in my Company we have a ip phone solution and therefore we can call without any costs. If we call a special number with our cellphones, the PBX calls back and then we can then enter the phone number of our target. in germany its usually called "MFV Töne senden" which means the phone sends dtmf tones. From any cellphone we use i can go into the phonebook(while the callback) and send DTMF tones. Every Phone exept my HTC Magic.
Is there a way to extend the phonebook(i think i have read about it, that its possible), but if not is it possible to write an app which sends the dtmf tones to the active call?
Thank you all, if that problem is solved our whole company will use android phones, what a charm!